This invention relates to an anisotropically electroconductive sheet and a process for producng the same. More particularly, this invention relates to an elastomeric sheet which is electroconductive in its thickness direction (Z direction) and non-conductive in the plane direction (XY direction), and to the process for producing same.
The aforementioned anisotropically electroconductive sheets are useful as connectors of electronic circuits, since they can connect many electrodes which are independently located on the directly opposite sides of the electroconductive sheet. They are especially useful as connectors in electronic calculators, cameras, wrist watches, etc., where circuit elements are confined to very limited spaces.
An elastomeric sheet which comprises alternate layers of conductive and non-conductive silicone rubber has been used in the past as an electronic connectors. However, use of this elastomeric sheet requires some restrictions on the disposition of the electrodes.
There is another type of elastomeric sheet that is known which has metal particles dispersed in the elastomer. This sheet is non-conductive in the uncompressed state but it becomes conductive only when it is compressed because the metal particles then contact each other. However, this conductivity depends on pressure and it is difficult to maintain the appropriate pressure for the period of time conductivity is needed.
On the other hand, U.S. Pat. No. 2,189,340 describes a conductive sheet which is used as an electrode for a television Braun tube. This sheet is made by orienting conductive wires or fibers in a transparent matrix, such as glass or rosin, and then hardening the matrix. Although this sheet is anisotropic, it is unsuitable for use as an electronic connector, since it is too hard. Also, this particular conductive sheet may have a rough surface which makes uniform electrical contact between conductors difficult.